1. Field of the Invention
The present invention relates to a semiconductor device fabrication method, and more particularly to an HF (hydrogen fluoride) cleaning technology used in the fabrication method.
2. Description of the Related Art
FIG. 1A and FIG. 1B of the accompanying drawings depict an acceleration sensor 20 which is formed by processing a silicon substrate. FIG. 1A is a perspective view and FIG. 1B is a partial cross-sectional view taken along the 1B-1B line in FIG. 1A.
This acceleration sensor 20 has an outer frame section 1a, a weight section 1b and beam sections 1c. These sections are integrated by processing a silicon substrate 1. The outer frame section 1a supports the weight section 1b formed at the center via the flexible four beams 1c. 
On the surface of each beam section 1c, an insulation film 2 made of SiO2 is formed, and piezo resistors 3 are provided on the insulation film 2. The resistance values of the piezo resistors 3 are changed according to the deflection of the beam sections 1c when displacement of the weight section 1b is caused by an acceleration. The piezo resistors 3 are connected to the pads 5 provided on the surface of the outer frame 1a by aluminum wires 4. The pads 5 are provided for connection to external devices.
The surfaces of the insulation film 2, piezo resistors 3 and aluminum wires 4 are protected by a protective film 6. The pads 5 are not protected (covered) by the protective film 6.
The acceleration sensors are fabricated by forming an insulation film 2, piezo resistors 3, aluminum wires 4 and pad 5 for each of many acceleration sensors on the silicon substrate 1, covering each insulation film 2 and other areas by a protective film 6, and removing the silicon between the outer frame section 1a and weight section 1b by etching for each acceleration sensor, so as to from a space between the outer frame section 1a and weight section 1b. The substrate is cut into individual sensors to have the acceleration sensor shown in FIG. 1A.
After forming the space section by etching, cleaning is performed to remove foreign substance attached to the surface of the outer frame section 1a and weight section 1b. This cleaning is performed using HF aqueous solution to remove SiO2 residue. In order to protect the insulation film 2, piezo resistors 3, aluminum wires 4 and pads 5 formed on the silicon substrate 1 from the HF aqueous solution (cleaning solution), the silicon substrate is covered with resist 11, as shown in FIG. 1B, and then the silicon substrate having the resist 11 thereon is dipped into the HF aqueous solution for cleaning.
This acceleration sensor is disclosed in Japanese Patent Application Laid-Open (Kokai) No. 2003-139791.
If the cleaning is carried out with the HF aqueous solution, the following problem arises. Because of insufficient adhesion between the silicon substrate 1 and resist 11, HF aqueous solution enters (filters into) the gap between the silicon substrate 1 and the resist 11, etches the insulation film 2, and corrodes the aluminum wires 4. As a result, the HF aqueous solution deteriorates qualities of the product.